1. Field of the Invention
The present invention relates to a water base ink for ink jet recording and a water base ink set for ink jet recording.
2. Description of the Related Art
In a case that high-speed printing is performed on recording papers by using a water base ink for ink jet recording containing water, water-soluble organic solvent and a coloring agent, the recording papers on which the recording has been performed (printed recording papers) are stored on a paper discharge tray such that a printed recording paper is overlaid on another printed paper on which the printing was performed before the printed recording paper. Therefore, in some cases, phenomenon called “transfer (ink transfer)” occurs that the ink on a surface of a printed recording paper dirties or stains the back surface of another printed recording paper printed after the printed recording paper and overlaid on the printed recording paper. To address this situation, it is a widely performed practice that glycol ethers are added to a water base ink for ink jet recording so as to enhance the permeability of the ink to the recording paper, consequently enhancing the drying performance of the ink on the paper surface.
However, if the permeability of the ink to the recording paper is excessively enhanced, this causes a phenomenon called “strike-through to the back surface (strike-through)” in which the ink permeates and arrives even at the back surface of the recording paper, in some cases. In such cases, it is feared that the printing density is lowered as a result. In particular, since a pigment ink is harder to permeate in the recording paper than a dye ink, there is a tendency that a penetrant is used for the pigment ink in an amount greater than that of the penetrant used for the dye ink. Therefore, the phenomenon of “strike-through” easily occurs in the pigment ink.
For the purpose of improving the abrasion resistance of a printed matter obtained by performing printing on a recording paper with a water base ink for ink-jet recording containing water, a water-soluble organic solvent and a pigment dispersion, Japanese Patent Application Laid-open No. 8-231910 proposes to add at least one of polysaccharose, cellulose derivative and modified starch, which are classified as so-called thickeners, at a relatively large blending amount of 3% by weight to 40% by weight with respect to the total amount of the ink.
However, the concentration of the thickener is too great in the water base ink for ink jet recording proposed by Japanese Patent Application Laid-open No. 8-231910. Therefore, in this water base ink for ink jet recording, the ink has a tendency to present (remain) locally on the surface of the recording paper or inside a portion of the recording paper in the vicinity of the paper surface, which in turn lowers the drying property of the ink on the paper surface, and consequently leads to a fear that the “transfer” might occur.